1. Field of the Invention
The present invention relates generally to the manufacture of cork-based stoppers, and more particularly to a process for treating a cork-based product which can be used to make stoppers.
The invention also relates to a stopper comprising this product, for closing bottles of alcoholic or non-alcoholic drinks such as, for example, still or sparkling wines, spirits, ciders and carbonated fruit drinks.
2. Description of the Related Art
The cork from which stoppers are manufactured is a plant tissue produced by the suberophellodermic stratum of cork oak.
It consists of dead cells of alveolar structure. These cells are filled with gas whose composition is very close to that of air.
Cork is composed essentially of about 45% suberin, which is the main constituent of the alveolar cells, about 27% lignin of fibrous structure, which is included in channels or at the surface of the bark, about 12% cellulose and about 17% of various other products such as ceroids, tannins, mineral materials and water.
Cork is a good material for stoppering and storing still or sparkling drinks, in particular wines or other bottled alcohols, since it is a material which is compressible and sufficiently elastic, leaktight and hydrophobic.
Cork contains about 5% water but becomes hydrated slowly.
It is just sufficiently gastight to allow wines or alcohols to age correctly without oxidizing.
However, cork is a natural material which has more or less major defects.
These defects consist mainly of channels with lignified walls or lignin inclusions.
They have a deleterious effect on the elasticity and leaktightness of the stopper.
In addition, they contain substances or precursors thereof which may, during aging, give the stoppered wines or alcohols unpleasant tastes known as xe2x80x9ccorked tastesxe2x80x9d.
Several studies have revealed certain substances contained in cork from which stoppers are made, which give rise to adverse changes to wine, giving it a corked taste.
The main substances identified are:
2,4,6-trichloroanisole (TCA),
2,5-dimethylpyrazine,
2-methylthio-3-ethylpyrazine,
4-ethylphenol,
2,6-dichlorophenol,
geosmine,
guaiacol,
1-octen-3-one,
1-octen-3-ol,
2-methylisobomeol.
These abovementioned substances give wine unacceptable aromas, even at low concentrations.
These substances or precursors thereof are located in the ligneous parts of cork. Thus, the TCA content in cork increases as the proximity to the bark of cork oak (lignified part) increases. Guaiacol is produced by the action of a bacterium on lignin. The other abovementioned substances have as precursors tannins, bacteria or molds which are preferentially in the lignin or the lignified channels.
The conventional process for treating cork for the purpose of manufacturing stoppers comprises a boiling operation carried out on cork sheets or cork barks dried for about 2 years. This operation consists in immersing said cork sheets or barks in a bath of boiling water at a temperature of about 100xc2x0 C. for about 1 h 30min.
This boiling operation is followed by a rest phase which ranges from 48 hours to three weeks approximately, in particular to stabilize the excess moisture in the treated product.
The cork plates or barks thus treated are then used in the stopper manufacturing line.
Besides the fact that this process for treating cork is very long, the rest phase is a critical step during which the cork may be contaminated with bacteria or molds, which may be the cause of the xe2x80x9ccorked tastexe2x80x9d.
In an attempt to eliminate the drawbacks associated with the defects of medium-quality and low-quality natural cork while at the same time maintaining a relatively low cost of manufacture of the stoppers compared with the solution which consists in manufacturing the stoppers using a noble natural cork free of defects, stopper manufacturers have produced agglomerated stoppers consisting of particles of medium-quality or low-quality cork and a binder or adhesive which ensures the cohesion of the stoppers.
Composite stoppers are also known, an example of which is disclosed in patent application FR-A-2 672 002.
Such a stopper consists mainly of a powder of ligneous plant material obtained in particular from cork, expanded plastic microspheres and a food adhesive.
However, although the agglomerated stoppers are cheap to manufacture, their physicochemical and mechanical properties are inferior to those of natural cork stoppers and they therefore cannot be used to store wines or alcohols which are to be aged in bottles.
Furthermore, just as with the abovementioned composite stoppers, the use of agglomerated stoppers does not eliminate the appearance of corked tastes in wines or alcohols bottled and stoppered with such stoppers.
To overcome the abovementioned drawbacks, the present invention proposes a novel process for treating cork-based products which can be used for making stoppers and which in particular eliminates the risks of appearance of corked tastes in bottled wines or alcohols.
More particularly, the process according to the invention comprises the following steps:
a) said product is placed in a leaktight container,
b) said product is subjected to the action of steam at a pressure of between 2xc3x97105 and 30xc3x97105 Pa for a period of between about 5 seconds and 5 minutes,
c) a depressurization is carried out to bring the inside of the container to atmospheric pressure,
d) the treated product is recovered.
The cork-based products used for this process may be sheets or pieces of cork, intermediate products such as granules, tubing waste, sorting waste or finished products such as stoppers and rejects.